1. Field of the Invention
This invention relates to a thixotropic urethane-base sealing material and, more particularly, to a non-sag type urethane-base sealing material which comprises a urethane-base polymer mixed with an anti-sag agent and an additive of a particular nature so as to increase the thixotropic property of the base polymer and to improve its processing ability along with its anti-sag property.
2. Description of the Prior Art
In general, thixotropic urethane-base sealing materials are broadly classified into one-package types and two-package types: the former includes as base polymer a urethane prepolymer having at its ends isocyanate groups which can be cured or hardened after its application by means of moisture in the air; and the latter includes as base polymer a urethane prepolymer having isocyanate groups at its ends and is cured by the addition of a polyether polyol or the like. The sealing materials of both types are widely employed for architectural use, for civil engineering and for direct glazing in motor vehicle industries. For application to horizontal areas such as a floor, a sealing material is usually required to be of the so-called self-leveling type which flows easily to spread and makes a smooth surface. On the other hand, for application to vertical areas such as wall surfaces or window frames, a sealing material is required to be of the non-sag type which is substantially free from sagging or slumping after application. That is, the non-sag type sealing material should flow easily by external forces during its mixing and application. However, when it is at a standstill, the material should show no substantial flowability, i.e., exhibit a thixotropic property, due to its extremely increased apparent viscosity.
Non-sag type urethane-base sealing materials as known in the art generally include a urethane prepolymer or mixture thereof with a polyol as a base polymer and a plasticizer, adhesion improver, catalyst and pigment or the like, together with a filler such as talc, calcium carbonate, carbon black, diatomaceous earth, titanium dioxide or the like. The filler contributes not only to increase the weight of sealing material but also to control the hardness of cured material. However, a sealing material which is obtained by mixing a base polymer and said filler alone exhibits an extremely great sagging or slumping tendency during the application thereof, so that to obtain a non-sag type sealing material, it is common practice to use colloidal silica as an anti-sag agent. In this connection, it is the common experience that the greater the amount of the anti-sag agent used, the greater becomes the thixotropic tendency of the mixture with an extremely large increase in the apparent viscosity of the mixture, resulting in considerable reductions in mixing or other operational efficiencies. Furthermore, as the amount of this agent is increased, the more seriously deteriorated are the physical properties of the sealing material obtained after curing or hardening, i.e., hardness and modulus are undesirably increased, coupled with a substantial reduction in elongation and adhesion strength. For this reason, the use of a great amount of an anti-sag agent is not desirable. However, there have been known in the art few, if any, anti-sag agents which are useful for a urethane sealing material in only a small amount.
It is therefore a primary object of the present invention to provide a urethane base sealing material which is superior in both processing and non-sag properties.
It is another object of the present invention to provide a urethane base sealing material prior to being hardened which has desirable physical properties after curing.
It is a further object of the present invention to provide anti-sag agents and additives which are effective in small amounts and in combination to prevent a urethane base sealing material from sagging in use.
Still further objects and the entire scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. It has been found that the above objects can be attained by practicing the present invention.
An intensive and comprehensive study on the thixotropic effects of various compounds on urethane-base sealing materials has been conducted and there have been found compounds which exhibit substantially no anti-sag or anti-slump property when used along but which remarkably improve thixotropic and anti-sag properties of a sealing material when employed in combination with an anti-sag agent such as colloidal silica. The present invention is based upon this finding.